1. Field of the Invention
Aspects of the present invention relate to a flat panel display using a signal transmission method for transmitting a differential signal, and more particularly, to a flat panel display incorporating a differential signaling system for impedance matching in the signal transmission method.
2. Description of the Related Art
In general, a cathode ray tube (CRT) is one type of display device that has been widely used. CRTs have been used as monitors for television sets, measuring instruments, or information terminals. Because a CRT is heavy and large, it cannot be used when miniaturization or light weight are design requirements.
Accordingly, in order to substitute for a CRT, various flat panel displays such as a liquid crystal display (LCD), a plasma display panel (PDP), a field emission display (FED), and an organic light emitting display (OLED) have been developed. These have the advantages of miniaturization, light weight, and low electric power consumption.
As cited above, a flat panel display includes various components as well as wiring for transmitting signals among the various components. Recently, with the development of electronic circuit and manufacturing process technology, a signal can be transmitted through the wiring at high speed. To meet high speed signal transmission requirements, the drive speed of the components has also become high.
Accordingly, various methods for transmitting signals among the components and through the wiring have been suggested. For example, a signal transmission method such as a low voltage differential signal (LVDS) method or a reduced swing differential signaling (RSDS) method for transmitting a differential signal has been used.
A differential signaling system transmits a different mode signal having the same amplitude and a different polarity through a differential transmission line. Accordingly, there is a tendency to remove a concentrated magnetic field and to couple an electric field. Because of the coupled electric field, a high speed signal can be stably transmitted without a signal reflection or skewed (phase delay) electro magnetic interference (EMI).
A conventional flat panel display will be described with reference in detail to FIGS. 1-3. FIG. 1 is a block diagram showing the structure of a conventional flat panel display. As shown in FIG. 1, the conventional flat panel display includes a display panel 40, a gate driver 20, a data driver 30, and a controller 10. Pixels are arranged in the matrix of the display panel 40. The gate driver 20 sequentially applies a scan signal to gate wires of the display panel 40. The data driver 30 applies an image signal DATA1 to data wires of the display panel 40. The controller 10 applies the image signal DATA1 from an external graphic controller (not shown) to the data driver 30, and applies a control signal CS1 to the gate driver 20 and the data driver 30 in order to control drive timing. In the conventional flat panel display, after all gate wires of the display panel 40 are sequentially scanned and the image signal DATA1 is applied to pixels through the data wires to display one frame of an image, a vertical synchronous signal VSYNC is applied to display the next frame of the image.
FIG. 2 is a block diagram showing in detail the controller and the data driver of FIG. 1. FIG. 3 is a block diagram showing a signal transmission method between the controller and the data driver. As shown in FIG. 2, the data driver 130 is composed of a plurality of data driving circuits 132. The plurality of data driving circuits 132 receives image signals DATA [+,−] from the controller 110 through first and second wires W1 and W2, and receives a control signal CS11 from the controller 110 through a third wire W3.
The data driver 130 includes a plurality of data driving circuits 132 therein. The data driving circuits 132 receive image signals DATA [+,−] from the controller 110, and output them to the data wires in response to the control signal CS11 from the controller 110. Although they are not shown in drawings, a plurality of data wires are electrically coupled to the data driving circuits 132, and apply the image signals DATA [+,−] that were applied to the data driving circuits 132 to the pixels.
The image signal from the controller is transmitted to the respective data driving circuits in the conventional differential signal transmission method. That is, as shown in FIG. 3, in order to transmit one data group DATA [+,−], a differential transmission line arrangement, namely, first and second wires W1 and W2 are provided between the controller 110 shown as a sending end Tx and the data driving circuit 132 shown as a receiving end Rx.
Meanwhile, a termination resistor Rt is installed between the differential transmission lines of the receiving end (data driving circuit 132). The termination resistor Rt electrically connects the first wire W1 and the second wire W2 that are connected to each data driving circuit 132 to each other.
In this way, the image signal DATA [+] applied through the first wire W1 is transferred from the controller 110 through the termination resistor Rt and the second wire W2. The termination resistor Rt prevents excess current from flowing to the data driving circuit 132 while the voltage across the termination resistor Rt is image signal DATA [+,−], which is applied to the data driving circuit 132.
A plurality of electric devices and wires are provided in the flat panel display, and are electrically coupled to each other. The electric devices and wires have an impedance component that attenuates the signal during signal transmission between the electric devices.
The controller 110 and the data driving circuits 132 also have an impedance component. Further, the first and second wires W1 and W2 for connecting the controller 110 and the data driving circuits 132 have an impedance component Z0.
If the impedance value Z0 of the first wires W1 and W2 is different from that of the data driving circuits 132, namely, when the impedances do not match, the image signals DATA[+,−] are not exactly supplied to the data driving circuits 132. That is, a portion of the image signals is reflected and discharged.
In detail, a reflection coefficient ┌ is expressed by a following equation 1:
                    Γ        =                                            Z              diff                        -                          R              t                                                          Z              diff                        +                          R              t                                                          (        1        )            where the differential impedance Zdiff is the sum of impedance values of the first and second wires, has a value less than 2Z0, and also has a different value depending on the manufacturing process and construction of the flat panel display.
Specifically, when the differential impedance Zdiff is identical to the value of the termination resistor, a reflection loss of a signal does not occur. However, because the differential impedance Zdiff varies, in the conventional case, impedance matching is not normally achieved in the differential transmission method.
Furthermore, when a reflection wave occurs due to impedance mismatching, electro-magnetic interference (EMI) with the image signals DATA [+,−] applied through the first wire W1 occurs and causes an unstable wave, signal distortion and attenuation. As a result, the EMI deteriorates image quality of the flat panel display.